JPH0323573Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an eddy current type tachometer.

In conventional tachometers of this type, a permanent magnet is rotated around a rotation axis in accordance with the rotational speed of the object to be measured, and the magnetic flux generated by this permanent magnet is cut and rotated around the axis of this rotation axis. A rotatable induction board is provided, and the induction board is caused to rotate in accordance with the rotational speed of the object to be measured based on the eddy current generated in response to the rotation of a permanent magnet, and a pointer is attached to the induction board. The speed (or rotational speed) is displayed in terms of rotation angle.

In such an eddy current type tachometer, in order to digitally detect and retrieve the speed or number of rotations separately from the analog display on the pointer, a reed switch is installed as a number of rotations sensor near the permanent magnet. The number of rotations of the rotating shaft may be digitally detected by detecting the magnetic field of each magnetic pole generated by the rotation of the magnet.

Figure 1 shows the configuration of a conventional eddy current type tachometer equipped with a reed switch as a rotational speed sensor.The center of the closed surface of the instrument box 1 has one of the end faces open. A mounting hole 2 is formed in the mounting hole 2, and a rotating shaft 3 is rotatably inserted into the mounting hole 2.
is pivoted. An open cylindrical body 5 having an outer diameter smaller than the outer diameter of the rotary shaft 3 is integrally formed on an end surface 4 of the rotary shaft 3 located inside the box 1 so that its axis coincides with the end face 4 of the rotary shaft 3. An attachment hole slightly larger than the outer diameter of the cylindrical body 5 is formed at the center thereof, and the cylindrical body 5 is fitted into the attachment hole of a shallow cylindrical holder 7 made of a non-magnetic material with one side open. A holder 7 is fixedly attached to the end surface 4 of the rotating shaft 3. A magnetic path structure 8 made of a magnetic material is attached to the entire inner peripheral surface of the holder 7. A disk-shaped permanent magnet 10 having an outer diameter slightly smaller than the inner diameter of the holder 7 to which the magnetic path structure 8 is attached is attached to the holder 7 . That is, an aperture 6 having a diameter slightly larger than the outer diameter of the cylindrical body 5 is formed at the center of the permanent magnet 10 on an extension of the rotating shaft 3, and the cylindrical body 5 is inserted into this aperture 6 to form a permanent magnet. 10 is attached to the holder 7. Permanent magnet 10 of cylindrical body 5
The upwardly protruding edge part is bent outward,
The permanent magnet 10 is fixed to the holder 7 at this bent edge portion.

One end of the rotation shaft 11 is inserted into a cylindrical body 5 formed continuously with the rotation shaft 3 . This rotation axis 1
One end of 1 is held within the cylindrical body 5 in frictionless contact with the cylindrical body 5. An induction disk 12 made of a conductive material is fixedly attached to this rotating shaft 11 so as to face the permanent magnet 10 . This guide plate 12 is formed into a cup shape in which the periphery of a disk is bent in the direction of the permanent magnet 10 at right angles to the disk, and this bent peripheral surface portion is used as an opposing surface facing the permanent magnet 10. An end of the rotating shaft 11 opposite to the cylindrical body 5 is arranged to protrude outside the box 1, and a pointer 13 is fixedly attached to the end. Box body 1
The open surface of the instrument is covered with a lid 14, and a dial 15 of the meter is fixed to the lid 14 and disposed between the lid 14 and the pointer 13. One end of the hairspring 16 is fixedly attached to the lid 14 in the box 1,
The other end of the balance spring 16 is connected to the lid body 14 and the guide plate 12.
It is attached and fixed to the rotating shaft 11 in between.

In the measuring state of the instrument, the hairspring 16
The rotation shaft 11 is in a state where it is rotationally biased in a certain direction by the biasing force of is adjusted and installed.

Holding pieces 27-1 and 27-2 are fixed to the closed surface of the box 1, and a reed switch 18 is mounted on the wiring board 17P supported and fixed to the holding pieces 27-1 and 27-2.
is arranged in the vicinity of the magnetic pole position of the permanent magnet 10 via the holder 7 so as to match the circumference of one concentric circle around the center of the permanent magnet 10 in its longitudinal direction. A rotating shaft of an object to be measured whose rotational speed is to be measured is connected to the rotating shaft 3 by means not shown.

Therefore, in the measurement state, the rotation of the object to be measured is transmitted to the rotating shaft 3, so that the holder 7 attached to the rotating shaft 3 within the box 1 rotates, for example, at the rotation speed of the object to be measured. It rotates in the direction shown by the arrow ω in Figure 2. The permanent magnet 10 emits S from its N pole.
Although lines of magnetic force are generated that reach the poles, most of these lines of magnetic force pass through the magnetic path structure 8 made of a magnetic material to form a closed magnetic path. The magnetic flux generated from the N pole of the permanent magnet 10 by the magnetic field H formed by this closed magnetic path passes through the induction plate 12 at right angles from the permanent magnet 10 side, passes through the magnetic path structure 8, and passes through the induction plate 12 again. It penetrates at right angles from the magnetic path structure 8 side and reaches the S pole of the permanent magnet 10.

In the example shown in FIG. 2, a magnet having four magnetic poles is formed along the periphery of the permanent magnet 10.
In this way, magnetic flux passes through the induction plate 12 at right angles due to the magnetic field H formed between the N pole and the S pole of the permanent magnet 10. Therefore, when a change occurs in the penetrating magnetic flux on the induction plate 12, the change occurs. Eddy currents are induced around the penetrating magnetic flux in a direction that impedes the flow. When the rotating shaft 3 rotates, for example, at a position on the induction plate 12 facing the magnetic pole, the penetrating magnetic flux changes in a direction such that it decreases, so an eddy current is generated in the right-handed screw direction that tries to prevent the change in the penetrating magnetic flux. arise.

Considering the component of this eddy current parallel to the rotation axis 3, since there is a magnetic field H perpendicular to the induction plate 12 at this position, the induction plate 12 has a component perpendicular to both the eddy current and the magnetic field H as shown in FIG. Electromagnetic force acts in the direction indicated by arrow F. This electromagnetic force F is proportional to the rate of change of magnetic flux, that is, the number of rotations of the rotating shaft 3 per unit time. Due to this electromagnetic force F, the guide plate 12 rotates in the same direction to follow the rotation of the rotating shaft against the biasing force of the hairspring 16. For this reason, the pointer 13 rotates in accordance with the rotational speed of the object to be measured, and this rotational angle is read by the code attached to the dial 15, and the rotational speed per unit time of the rotating shaft is determined. be measured. Therefore, for example, by connecting the rotation of the vehicle's wheels to the rotating shaft 3 and detecting the number of rotations per unit time by the rotating shaft 3, the traveling speed of the vehicle can be displayed.

A reed switch 18 as a rotational speed sensor is disposed close to the permanent magnet 10 with its longitudinal axis extending along the circumferential direction of one concentric circle of the permanent magnet 10. Therefore, as the permanent magnet 10 rotates, the reed switch 18 is turned on at a position of the permanent magnet 10 where the magnetic field from the permanent magnet 10 passes between both ends of the reed switch 18, and the magnetic field passes between both ends of the reed switch 18. In other words, as shown in FIG. 3, the permanent magnet 1
The reed switch 18 is in the OFF state at the position where the zero magnetic pole is present on the reed switch 18. Therefore, a quadrupole permanent magnet 10 as shown in FIGS. 2 and 3
When using the reed switch 18, the reed switch 18 repeats ON-OFF four times with one rotation of the permanent magnet 10, so if the ON-OFF of the reed switch 18 is taken out as an output signal, one rotation of the permanent magnet 10 will produce an output signal of four pulses. Since the number of pulses detected by the reed switch 18 and taken out as an output signal is proportional to the rotation speed of the rotating shaft 3, the rotation of the vehicle's wheels is connected to the rotating shaft 3, and the number of pulses detected by the reed switch 18 and taken out as an output signal is If the pulse is detected every unit time, this output signal can be extracted and used as vehicle speed information.

In the conventionally used eddy current type rotation speed, it may be necessary to divide the output signal pulse of the reed switch 18 as a rotation speed sensor in order to use it as speed information and perform various calculations. . Conventionally, this rotation speed sensor 2
If a pulse/one revolution output signal is required, a separate frequency dividing circuit is provided and the four pulse/one revolution output signal of the reed switch 18 is guided to this frequency dividing circuit to divide the number of pulses electronically. Was. For this reason, frequency division of the output signal of the rotation speed sensor of the conventional eddy current type tachometer requires a complicated circuit, which has the disadvantage that the entire device becomes large-scale.

As a mechanical method, as shown in FIG. 4, a two-pulse/one-rotation output signal is obtained from the reed switch 10 by imparting two-pole magnetization to the permanent magnet 10. The method using a cylindrical magnet as shown in FIG. 4 causes a shortage of torque generated in the induction plate 12. For this reason, the lack of torque was resolved by changing the shape and improving the material as shown in Figure 5. For this reason, there were disadvantages such as an increase in costs, the occurrence of foreign products in the assembly process, and the impossibility of standardizing the mechanism. In order to solve these difficulties, it becomes necessary to make the permanent magnet 10 cylindrical and magnetize it with four poles or six poles as in the conventional case.

Therefore, the applicant of the present application first resolved the above-mentioned difficulties with the conventional eddy current type tachometer, and by changing the magnetic pole arrangement position of the permanent magnet, it is possible to achieve highly accurate frequency division of the detection output signal by the rotation speed sensor. We are proposing an eddy current type tachometer.

FIG. 6 is a diagram showing the magnetization state of the permanent magnet 10 used in the tachometer proposed above. In the magnetization shown in the figure, two sets of S-N poles are formed on mutually orthogonal lines passing through the center of rotation of the permanent magnet. Therefore, the rotation axis 3
When the quadrupole-magnetized permanent magnet 10 rotates with the rotation of the reed switch 18, the
-The reed switch is placed in a position opposite to group N twice, and the reed switch is operated twice for each rotation of the rotating shaft 3.

In other words, the output signal pulse of the reed switch as a rotation speed sensor is 1/2 of the output signal pulse of the reed switch of the conventional device, which is 2 pulses/1.
Rotation is achieved.

By the way, this four-pole magnetization can be carried out using a magnetizing machine having four coils as shown in FIG. 7, but the same-polarity coils interfere with each other and the magnetization distribution becomes as shown in FIG. 8. This distribution was not much different from the distribution of the cylindrical magnet shown in FIG. 4, and a sufficiently large torque generated in the induction disk 12 could not be obtained, which caused a practical problem.

The present invention was made in order to eliminate the problems of the conventional ones mentioned above.The purpose of this invention is to provide a lead by one rotation of the 4-pole permanent magnet without impairing the rotational torque of the induction plate by the permanent magnet. An object of the present invention is to provide an eddy current type tachometer that generates two pulses by operating a switch.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 9 shows the magnetization distribution of the permanent magnet used in the tachometer according to the present invention, and the permanent magnet is magnetized so that the magnetic poles on lines that are orthogonal to each other through the center of rotation are different. , and are magnetized so that the magnetic flux distribution between mutually adjacent magnetic poles of the same polarity is approximately zero.

When a permanent magnet with such a magnetic flux distribution is used, the reed switch is turned on twice by one rotation of the permanent magnet, as in the case described above with reference to FIG.
2 by one rotation of the permanent magnet by turning it off.
It is possible to generate two pulses. Moreover,
Since the magnetic flux distribution between the same magnetic poles is approximately zero, clear quadrupolar magnetization is occurring, and as a result, the permanent magnet described above with respect to FIGS. 2 and 3, that is, the center of rotation The same torque can be obtained as if the same magnetic poles were arranged on mutually orthogonal lines.

FIG. 10 shows an example of a magnetizing device for obtaining a permanent magnet having the magnetic flux distribution shown in FIG.
The structure is such that coils 32a, 33a, 34a and 35a are wound around four cores 32, 33, 34 and 35, which are formed into zero, respectively. In addition, core 3
2, 33, 34, and 35 are located on lines that pass through the center O of the frame 30 and are orthogonal to each other, and the polarities at opposing positions are different. In the illustrated example, the core 32 is the south pole, and the core 34 opposite thereto is the north pole.

Then, auxiliary cores 37 and 38 are provided between the coils 32a and 35a of the same polarity and between the coils 33a and 34a, respectively, and the coils on both sides and the coils 37a and 38a of different polarity are wound respectively. be. That is, the coils 37a and 38a change the magnetic field distribution between the N and N poles or between the S and S poles, for example, if the magnetic field is on the north pole side, it is shifted to the south pole side, and if the magnetic field is on the south pole side, it is shifted to the north pole side. It is designed to attract and bring it extremely close to zero.

As explained in detail above, according to the eddy current type tachometer of this invention, by changing the magnetic pole arrangement position of the permanent magnet, the number of revolutions can be easily, inexpensively, and accurately obtained without changing the conventional structure and without causing insufficient torque. This makes it possible to divide the sensor output signal with high precision, and has great industrial significance.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a conventionally used eddy current type tachometer, Figures 2 and 3 are diagrams showing the operating principle of the eddy current type tachometer, and Figures 4 and 5 are conventionally used eddy current type tachometers. Figure 6 shows the magnetization state of the permanent magnet used in another example of the conventional eddy current type tachometer and the operating and non-operating states of the reed switch. 7 is a diagram showing a magnetizing device that obtains the permanent magnet shown in FIG. 6, FIG. 8 is a graph showing the magnetic flux distribution of the permanent magnet obtained by the magnetizing device shown in FIG. 7, and FIG. 9 is a diagram showing a magnetizing device that obtains the permanent magnet shown in FIG. 10 is a graph showing the magnetic flux distribution of a permanent magnet used in the tachometer according to the present invention, and FIG. 10 is a diagram showing a magnetizing device for obtaining a permanent magnet having the magnetic flux distribution shown in FIG. 9. 1...Box body, 2...Mounting hole, 3...Rotating shaft, 10...Permanent magnet, 12...Induction board, 13...
...Pointer, 18...Reed switch.

Claims (1)

[Scope of utility model registration request] a permanent magnet that rotates together with a rotating shaft that is rotatably attached to a box; and an induction board that is rotatably disposed near and opposite the permanent magnet around the axis of the rotating shaft; a pointer attached to the induction board, the permanent magnet is magnetized so that the magnetic poles on lines that are orthogonal to each other through the center of rotation thereof are different from each other, and the rotation of the permanent magnet is caused by the rotation of the permanent magnet. A rotating torque proportional to the number is outputted to the induction board to drive the pointer, and a magnetic field generated by the permanent magnet turns on and off a reed switch disposed near the permanent magnet inside the box. An eddy current type tachometer according to the present invention, wherein the permanent magnet is magnetized so that the magnetic flux distribution between mutually adjacent magnetic poles of the same polarity is approximately zero.